Don't use grouping_keys for cache and traffic.
Don't use grouping_keys for cache and traffic.

See https://bugs.chromium.org/p/chromium/issues/detail?id=781899#3.
Since PageCyclerStory is the only page that uses this, instead just do
this there. This sets the stage for deprecating grouping_keys (page
names and tags should be enough).

See related chromium CL (should be committed first):
https://chromium-review.googlesource.com/c/chromium/src/+/757239

Bug: catapult:#4030
Change-Id: I3c75dc8eeb32980a67840f646ec191bf8162cfdb
Reviewed-on: https://chromium-review.googlesource.com/757504
Commit-Queue: Caleb Rouleau <58bdb6276c01e3ed53e660bf706aa902204feb0d@chromium.org>
Reviewed-by: Ned Nguyen <8e49e083cfcfb68517585b2e78d68c2fd2b70562@google.com>
Reviewed-by: Kunihiko Sakamoto <b8d96d1b0e8920eaf02b79b8aafd21fb9598f0af@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult